1. Field of the Invention
The invention relates to a composite wire, preferably of small diameter and high mechanical resistance, comprising a carbon-steel core and a stainless-steel outer layer.
2. Discussion of the Background
Fine wires, with diameter less than I mm, having a tensile strength in excess of 2000 MPa, used to manufacture, for example, guy wires, cables for the reinforcement of conveyor belts or pipes under pressure, elastomer reinforcement wires or cables, in general are obtained by fine wiredrawing of a machine wire made of high-carbon steel containing approximately 0.8% carbon, 0.5% manganese, 0.3% silicon, the remainder being essentially iron. These wires have the disadvantage of being sensitive to corrosion, which leads to risks of premature breaking in service. This problem of corrosion resistance also exists for wires of greater diameter, and it has been proposed to remedy it by using composite wires comprising a core made of high-carbon steel identical to that which has just been described, and a thin outer layer made of austenitic stainless steel of the SUS 304 type containing 17% to 19% chromium, 9% to 11% nickel, approximately 0.1% carbon, the remainder being iron and impurities resulting from processing. This is the case, in particular, in Japanese patent applications JP 56 148410 and JP 56 152922. But the solutions proposed by these patent applications do not make it possible to obtain diameters less than 1 mm and tensile strengths in excess of 2000 MPa. These limits result, in particular, from the formation of chromium carbides at the interface between the high-carbon steel and the stainless steel at the time of the thermal treatments required for wiredrawing.
In order to limit the detrimental effect of the chromium carbides at the interface between the high-carbon steel and the stainless steel, it has been proposed, in Japanese patent application JP 41 87336, to intercalate a fine layer of copper between the high-carbon steel and the stainless steel. There thus may be obtained a wire with a diameter of 0.7 mm, the tensile strength of which is 2000 MPa. But, with this technique, it is not possible to obtain a lesser diameter and a higher resistance; in addition, this technique requires the depositing of a layer of copper on the high-carbon steel core, which complicates manufacturing.